A STUDY ON THE SCOPE OF THE PHOTOCHEMICAL RING CONTRACTION OF SUBSTITUTED 2-AMINO-3-CYANO-4H-PYRANS TO CYCLOBUTENES - CRYSTAL-STRUCTURE OF O-1-ETHOXYCARBONYL-4-ISOPROPYL-2-PHENYLCYCLOBUTENE

A study on the influence of substitution on the photochemical reactivi ty of a series of differently substituted 2-amino-4H-pyrans 10a-h has been carried out, All of the compounds undergo ring contraction to the corresponding cyclobutenes 11a-h on direct irradiation, Variable amou nts of the enamides 12 and the alkynes 13 were also obtained, as secon dary photoproducts, The results obtained show that the cyclization tak es place in reasonable yields with alkyl, phenyl and hydrogen substitu tion at C-4 and at C-6, Cyano, ethoxycarbonyl and benzoyl substitution at C-5 also promotes the reaction, A high degree of stereochemical co ntrol was observed in most cases, The molecular geometry of cyclobuten e 11a, has been established by X-ray diffraction analysis. This study also shows that the crystal packing is formed by a system of chains li nked by strong hydrogen bonds.